Fehlermeldung bei Update

# deb cdrom:[Ubuntu-Server 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main restricted

#deb cdrom:[Ubuntu-Server 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main restricted

# See http:{{comment_single_line_double_slash:0}}
# newer versions of the distribution.
deb http://de.archive.ubuntu.com/ubuntu/ focal main restricted
# deb-src http:{{comment_single_line_double_slash:1}}

## Major bug fix updates produced after the final release of the
## distribution.
deb http://de.archive.ubuntu.com/ubuntu/ focal-updates main restricted
# deb-src http:{{comment_single_line_double_slash:3}}

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://de.archive.ubuntu.com/ubuntu/ focal universe
# deb-src http:{{comment_single_line_double_slash:5}}
deb http://de.archive.ubuntu.com/ubuntu/ focal-updates universe
# deb-src http:{{comment_single_line_double_slash:7}}

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://de.archive.ubuntu.com/ubuntu/ focal multiverse
# deb-src http:{{comment_single_line_double_slash:9}}
deb http://de.archive.ubuntu.com/ubuntu/ focal-updates multiverse
# deb-src http:{{comment_single_line_double_slash:11}}

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://de.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse
# deb-src http:{{comment_single_line_double_slash:13}}

## Uncomment the following two lines to add software from Canonical's 
## 'partner' repository. 
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http:{{comment_single_line_double_slash:15}}
# deb-src http:{{comment_single_line_double_slash:15}}

deb http://security.ubuntu.com/ubuntu focal-security main restricted
# deb-src http:{{comment_single_line_double_slash:17}}
deb http://security.ubuntu.com/ubuntu focal-security universe
# deb-src http:{{comment_single_line_double_slash:19}}
deb http://security.ubuntu.com/ubuntu focal-security multiverse
# deb-src http:{{comment_single_line_double_slash:21}}

# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom" 
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.